The Alpha SLT-A33 inherits the Handheld Twilight mode from recent Sony cameras. This fires-off six frames in quick succession and stacks them into a single image in an attempt to lower noise levels.

On this page we've put the SLT-A33's Handheld Twilight mode to the test. This automatically selects the sensitivity so we've compared it against the closest manual ISO setting in traditional modes.

The image above was taken with the Sony Alpha SLT-A33 using its Handheld Twilight (HHT) mode. The camera automatically selected an exposure of f4 / 1/40 and a sensitivity of 500 ISO; the original file measured 3.31MB. Since the PASM modes on the A33 only allow single stop sensitivity increments, we selected the closest setting of 400 ISO for our comparison below. We matched the aperture of f4 in Aperture Priority, although the A33 selected a shutter speed of 1/20 to go with it – this is one stop difference in shutter speed from the HHT mode, despite a smaller sensitivity difference of just 1/3 EV.

With an exposure that's effectively 2/3 of a stop longer (once sensitivity is taken into account), it's not surprising to find the Aperture Priority sample a little brighter than the one delivered automatically in HHT mode. You may also think that the Aperture Priority sample at 400 ISO would have almost insignificant noise levels, but look closely and you'll see the tell-tale textures in the background, along with slightly rough edges around details.

In contrast the HHT crops are bereft of noise with a very smooth finish. This smoothness initially gives the impression of noise reduction, but look closely and both sample contain roughly the same amount of detail – it's just that the HHT version essentially has no noise to speak of, while also avoiding the rough edges of the normal sample.

This is an impressive start for the A33's HHT mode. You may have expected it to only really deliver a benefit at higher sensitivities, but even compared to the camera shooting at 400 ISO, it's delivered a preferable result – and lest we forget it also did so with a slightly higher sensitivity, allowing a quicker shutter speed to better avoid camera shake. Like previous tests with HHT, it may have arguably under-exposed a tad, but it remains a valuable ally in low light.

The only downside to HHT is that it's fully automatic. This may annoy enthusiasts who prefer greater control over the settings – after all, HHT may reduce noise levels, but it's like you're shooting in Auto mode. New to the Sony Alpha SLT-A33 over previous models is Multi-frame Noise Reduction, which can be selected for any sensitivity in any standard mode, while also extending the range to 25,600 ISO. It's certainly exciting stuff, and you can see it in action in our Sony Alpha SLT-A33 Multi Frame Noise Reduction results page.

In this second example we've moved to the bar-setting seen in our Sample Images pages to see how Handheld Twilight mode copes with a common low-light situation.

The image on the left was taken with the Sony Alpha SLT-A33 using its Handheld Twilight mode. The camera automatically selected an exposure of f3.5 / 1/30 and a sensitivity of 1000 ISO; the original file measured 4.18MB. Since the PASM modes on the A33 only allow single stop sensitivity increments, we selected the closest setting of 800 ISO in Program mode, with the camera choosing an exposure of f5 / 1/15. As above, this represents another slight under-exposure from HHT in comparison to shooting normally in the PAS modes.

The crops below tell a similar story to our first example. Putting aside the minor difference in brightness, the HHT mode has delivered a very smooth result, eliminating the rough edges and noise textures of the single exposure. In contrast, the shot taken in Program mode with a fixed sensitivity of 800 ISO is quite patchy in areas – it's not at all bad, but the HHT version is much preferred, and again the HHT version was actually taken with a slightly higher sensitivity.

As we've seen on previous reviews, Sony's Handheld Twilight mode effectively reduces noise without compromising detail. As such we consider it not just a highly valuable facility to have at your disposal, but pretty much a no-brainer to use at higher sensitivities for static subjects.

As mentioned above, the only downside to HHT is its fully automatic operation, with the camera selecting the sensitivity, shutter speed and aperture as it sees fit. Enthusiasts will have to let go of all exposure control with HHT mode, but the SLT-A33 now offers an alternative. Each of its sensitivities, including an extended option of 25,600 ISO, can be selected with Multi-frame Noise Reduction, which like HHT mode, combines multiple exposures to reduce noise. The difference is you can choose the sensitivity it's applied to, along with setting the exposure. It's certainly exciting stuff, and you can see it in action in our Sony Alpha SLT-A33 Multi Frame Noise Reduction results page.